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https://issues.apache.org/jira/browse/CALCITE-3763?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Jin Xing reassigned CALCITE-3763:
---------------------------------
Assignee: Jin Xing
> RelBuilder.aggregate should prune unused fields from the input, if the input
> is a Project
> -----------------------------------------------------------------------------------------
>
> Key: CALCITE-3763
> URL: https://issues.apache.org/jira/browse/CALCITE-3763
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Jin Xing
> Priority: Major
>
> {{RelBuilder.aggregate}} should prune unused fields from the input, if the
> input is a {{Project}}.
> Pruning fields during the planning process is desirable, but often cannot do
> it - we are applying a {{RelOptRule}} that has to return the same fields, or
> we don't want to add an extra Project do so the pruning. But when we are in
> {{RelBuilder.aggregate}} and the input is a Project, neither of those
> limitations apply. We already have a Project, we are just making it narrower;
> and we know what fields the {{Aggregate}} will produce.
> For example,
> {code:sql}
> SELECT deptno, SUM(sal) FILTER (WHERE b)
> FROM (
> SELECT deptno, empno + 10, sal, job = 'CLERK' AS b
> FROM emp)
> GROUP BY deptno
> {code}
> becomes
> {code:sql}
> SELECT deptno, SUM(sal) FILTER (WHERE b)
> FROM (
> SELECT deptno, sal, job = 'CLERK' AS b
> FROM emp)
> GROUP BY deptno
> {code}
> If there are no fields used, remove the {{Project}}. (A {{RelNode}} with no
> fields is not allowed.)
> {code:sql}
> SELECT COUNT(*) AS C
> FROM (
> SELECT deptno, empno + 10, sal, job = 'CLERK' AS b
> FROM emp)
> {code}
> becomes
> {code:sql}
> SELECT COUNT(*) AS c
> FROM emp
> {code}
> Add an option {{RelBuilder.Config.pruneInputOfAggregate}}, default true, so
> that people can disable this rewrite if it causes problems.
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